We're engaged in pure speculation. After Hiroshima and Nagasaki, the war was over, every city in Japan levelled, not much need for ramping up production of nuclear weapons.
Instead of Hiroshima and Nagasaki, maybe it would have been Berlin and Frankfurt. The Germans would have caved, no one would have gambled on what America's nuclear production capacity might be.
Frankly, you are simply begging the question now. You keep saying that Germany would have won because it would have won. Even I have conceded that we are speculating about an alternative history which never happened. You haven't given a plausible explanation for how a much smaller country such as Germany, with far fewer people, resources, and industrial capacity could have defeated the US. We did, after all, destroy their infrastructure rather thoroughly and rather easily. The only thing certain was that they were on their way to victory over the Allies before the US joined the war.